Listeners with sensorineural hearing loss experience significantly more masking and significantly less release from masking than do listeners with normal hearing sensitivity. When background noise is intermittent, normal- hearing (NH) listeners take advantage of the momentary dips in the noise to understand the target signal. This benefit is termed masking release (MR). Hearing-impaired (HI) listeners do not experience the same degree of MR as NH listeners. As a result, HI listeners cannot understand speech in noisy environments at the same signal-to-noise ratios in which NH listeners can understand successfully. At the same time, listeners with hearing loss frequently complain that their amplification devices are not satisfactory in background noise. We propose to further our understanding of the masking and MR experienced by listeners with hearing loss and to investigate the causes and potential sources of remediation. In Experiment 1 we will test MR in speech recognition experiments across a wide range of noise and signal levels and bandwidths. We will test NH and HI listeners, as well as NH listeners whose thresholds will be elevated by noise to match those of the HI listeners. We will measure listeners' sentence recognition in quiet, steady noise, and fluctuating noise and will define MR as the performance difference between steady and fluctuating noise. We hypothesize based on preliminary results that signal audibility will not fully explain the reduced MR of HI listeners, and that additional variability is explained by HI listeners' reduced access to spectrotemporal information about the speech in the dips of noise. We further hypothesize that underlying changes in cochlear physiology can explain HI listeners' difficulty in conditions of intermittent noise, and we propose to measure cochlear function in Experiment 2. We will measure basilar membrane input/output responses, masking period patterns, modulation masking, and frequency selectivity to describe HI listeners' cochlear function. We will use results from Experiment 2 to compute the adjusted effective audibility experienced by HI listeners taking into account the loss of cochlear gain experienced by HI listeners. In Section 3 we will model and simulate the effects of cochlear hearing loss based on speech recognition and psychoacoustic test results obtained from the same listeners. We hypothesize that these models and simulations will provide accurate and useful predictions of MR in young HI listeners. We will use the resulting models and simulations as empirically based first steps in evaluating signal processing for noise reduction. In later years the models can also be applied further to listeners with severe hearing loss, and to elderly listeners with hearing loss. Overall, the findings will contribute to our understanding of the nature of hearing loss, the effects of reduced audibility and cochlear gain, and the implications for understanding speech in a variety of noise backgrounds. We hypothesize that improving our understanding of the nature of reduced masking release will improve our ability to develop signal processing algorithms that can more effectively remediate HI listeners' difficulties in noise. PUBLIC HEALTH RELEVANCE Results from the proposed experiments and models will help understand hearing-impaired listeners' difficulty understanding speech in background noise. We anticipate that models developed in this project will lay the groundwork for evaluating signal-processing algorithms to maximize speech intelligibility in noise.